The present invention relates to the coating of medical devices intended for in vivo deployment and, in particular, it concerns a method and device, which is suitable for use in an operating theater just prior to implantation, for selectively applying a medical coating to an implantable medical device, for example a stent.
The practice of coating implantable medical devices with a synthetic or biological active or inactive agent is known. Numerous processes have been proposed for the application of such a coating. Soaking or dipping the implantable device in a bath of liquid medication is suggested by U.S. Pat. No. 5,922,393 to Jayaraman, soaking in an agitated bath, U.S. Pat. No. 6,129,658 to Delfino et al. Devices introducing heat and/or ultrasonic energy in conjunction with the medicated bath are disclosed in U.S. Pat. No. 5,891,507 to Jayaraman and U.S. Pat. No. 6,245,104 B1 to Alt. The device of U.S. Pat. No. 6,214,115 B1 to Taylor et al. suggest spraying the medication by way of pressurized nozzles.
Initially such coating were applied at the time of manufacture. For various reasons such as the short shelf life of some drugs combined with the time span from manufacture to implantation and the possible decision of the medical staff involved concerning the specific drug and dosage to be used based on the patient's at the time of implantation, have lead to methods and devices for applying a coating just prior to implantation. Wrapping the implantable device with medicated conformal film is disclosed in U.S. Pat. No. 6,309,380 B1 to Larson et al. Dipping or soaking in a medicated bath just prior to implantation are suggested in U.S. Pat. No. 5,871,436 to Eury, U.S. Pat. No. 6,106,454 to Berg et al., and U.S. Pat. No. 6,1171,232 B1 to Papandreou et al. U.S. Pat. No. 6,203,551 B1 to Wu provides a bathing chamber for use with specific implantable device such as the stent deployed on the balloon of a catheter (FIG. 1).
Each of the methods and devices intended for use just prior to implantation, listed above, deposit the coating material onto any and all surfaces that are exposed to the coating. This may result in depositing coating material on surfaces on which the coating is unwanted or undesirable. Further, the coating may crack or break away when the implantable device is removed from the implantation apparatus. An example of this would be a stent deployed on a catheter balloon. As the balloon is inflated and the stent is expanded into position, the coating may crack along the interface between the stent and the balloon. These cracks may lead to a breaking away of a portion of the coating from the stent itself. This, in turn, may affect the medicinal effectiveness of the coating, and negatively affect the entire medical procedure.
It is further know to use Ink-Jet technology to apply a liquid to selected portion of a surface. In the paper “Applications of Ink-Jet Printing Technology to BioMEMS and Microfluidic Systems,” presented at the SPIC Conference on Microfluidics and BioMEMS, October, 2001, the authors, Patrick Cooley, David Wallace, and Bogdan Antohe provide a fairly detailed description of Ink-Jet technology and the range of its medically related applications (http://www.microfab.com/papers/papers_pdf/spie_biomems.sub.-01_reprint.pdf). A related device is disclosed in U.S. Pat. No. 6,001,311 to Brennan, which uses a moveable two-dimensional array of nozzles to deposit a plurality of different liquid reagents into receiving chambers. In the presentation of Cooley and the device of Brennan, the selective application of the material is based on an objective predetermined location of deposit rather that on a subjective placement as needed to meet the requirements of a specific application procedure. With regard to the application of coatings applied to medical devices with ink-jet applicators, while it is possible to coat only a chosen portion of a device, such as only the stent mounted of a catheter, but not the catheter itself. This type of procedure using current device may, however, require providing complex data files, such as a CAD image of the device to be coated, and insuring that the device be installed in the coating apparatus in a precise manner so as to be oriented exactly the same as the CAD image.
Of most relevance to the present invention is U.S. Pat. No. 6,645,547 to Shekalim, et al., which is incorporated by reference for all purposes as if fully set forth herein. Shekalim, et al. teaches a system and method for selectively applying a coating to an implantable medical device, such as a stent, and thereby avoiding coating the balloon. Shekalim, et al. teaches inserting the stent while mounted on a balloon on a catheter into the device for coating. Since the stent is coated in its compact state after assembly on the balloon, problems of damage to the coating during collapsing of the stent onto the balloon are avoided. The system includes a drop-on-demand inkjet print head, which selectively coats the stent and avoids coating the balloon. The catheter is rotated past the drop-on-demand inkjet print head in order to coat the stent. Due to cost considerations of the system, the print head as well as the other elements of the system are not disposable. A shortcoming of the aforementioned system is that, due to sterility considerations, it is desirable that the elements coming into contact with the stent be disposable. A further shortcoming of the aforementioned system is that the stent is rotated around the print head and therefore the whole catheter needs to be rotated. Therefore, the system needs to be a large “tabletop” system which is typically not portable. If the system were miniaturized sufficiently to be portable, there would be an additional risk of the device being used in the wrong orientation which would compromise operation of the print head and could thus adversely impact the coating quality.
There is therefore a need for a portable stent coating system which avoids pre-expansion of the stent as well as avoids coating the balloon, where the elements coming into contact with the stent are low cost and therefore disposable.